Connection error because admin database is too big

Please, help
We’ve be been using mongo.db for more than a year and have many customers.
Suddenly, it shows connection error:

If we try to start from robo 3T, it shows: Error: Authentication failed.

If we start from command prompt:
C:\Program Files\MongoDB\Server\4.4\bin>mongo --host --username “xxxx” --password “yyyyyy”
MongoDB shell version v4.4.1
connecting to: mongodb://
Error: BSONObj size: 16793989 (0x1004185) is invalid. Size must be between 0 and 16793600(16MB) First element: _id: “admin.myname” :
exception: connect failed
exiting with code 1

We think that our admin database became too big, because we have to many collections and too many roles for all of them, so it became bigger than 16 mb.

We cannot connect to our mongodb on our server to see the size of it, or try tu reduce it’s size.
Is there anything we can do?


Forgot to mention: we don’t have a backup of the admin database.